Transmitter and receiver using non-adjacent component interleaving

ABSTRACT

A transmitter for transmitting information has a mapper for generating a plurality of mapped symbols, each mapped symbol having a first component and a second component, one of the first and second components being an in-phase component and the other of the first and second components being a quadrature component from a codeword; and a component interleaver for generating a plurality of interleaving units to be transmitted in a time sequence, the plurality of interleaving units consisting of at least three different interleaving units, wherein an interleaving unit has a plurality of pairs of first and second components, wherein the component interleaver is configured for assigning all first components and all second components of a codeword to the plurality of interleaving units in accordance with an interleaving rule, so that an I component of an mapped symbol and the Q component of the same mapped symbol are never assigned to one and the same interleaving unit, but to two different interleaving units.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of copending InternationalApplication No. PCT/EP2012/060895, filed Jun. 8, 2012, which isincorporated herein by reference in its entirety, and additionallyclaims priority from European Applications No. EP 11170186.8, filed Jun.16, 2011, and EP 11181660.9, filed Sep. 16, 2011, which are alsoincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

DVB-T2 as described in the DVB-T2 standard “Digital Video Broadcasting(DVB); frame structure channel coding and modulation for a secondgeneration digital terrestrial television broadcasting system (DVB-T2)”,ETSI EN 302 755 V1.1.1 discloses a plurality of so-called “modcods”. Amodcod is a pair consisting of a modulation/signal constellation such asQPSK, 16-/64-/256-QAM and code rates (1/2, 3/5, 2/3, 3/4, 4/5, 5/6).Each modcod has associated a spectral efficiency. The spectralefficiency is, for example, for a modcod of 16-QAM and a code rate of2/3 as follows: 4 codebits/symbol*2 infobits/3 codebits=8/3infobits/symbol=2.67 bits/s/Hz. Additionally, a constellation rotationincluding a coordinate interleaving can occur subsequent to the mappingof codebits. This procedure is, for example, disclosed in “JonathanStott: ‘Rotated Constellations’ available fromhttp://www.dtg.org.uk/dtg/t2docs/RotCon_Jonathon_Stott_BBC.pdf”. Theadvantage of such a constellation rotation is a higher diversity whentransmitting the coded signal which has been mapped to a certain signalconstellation. This results in a higher robustness for a given modcodand a spectral efficiency provided by the given modcod.

The DVB-NGH (Next Generation Handheld) standard is very similar to theDVB-T2 standard and shares many of its blocks. Among others, it supportsa large deal of the modcod parameters of DVB-T2, and it provides theoption for constellation rotation and coordinate interleaving.

Typically, a DVB transmission comprises an FEC encoder for applying acertain forward error correction code to an information word. Aninformation word may, for example, consist of 10,000 bits andadvantageously consists of, for example, 1,000 bits to 100,000 bits.Depending on the code rate, the FEC encoder generates a codeword fromthe information word. When there is a code rate of, for example, 1/3,the codeword consists of 30,000 bits when the information word has10,000 bits. For example, when the information word has 100,000 bits,then the codeword will have 300,000 bits. The bits of the codeword areintroduced into a subsequent bit interleaver. The bit interleaverperforms an interleaving within the codeword only, i.e. the for example300,000 bits within an encoded codeword are interleaved so that aninterleaved codeword results, but bits from one codeword are notinterleaved with bits of a different codeword. Then, subsequent to thebit interleaver, an interleaved codeword having codebits exists. Thecodebits are grouped depending on a certain constellation diagramapplied in a constellation mapping procedure. When the constellationdiagram is, for example, a 256-QAM constellation diagram, then groups of8 codebits are formed in order to map this group of 8 codebits into aconstellation symbol. In 64-QAM, only 6 bits are grouped and mapped toone of the 64 different QAM symbols. Depending on the implementation, aconstellation rotation and a cyclic Q-delay can be applied to theindividual symbols in order to obtain individual cells. However, theconstellation rotation or the cyclic Q-delay can be dispensed with sothat the symbols output by the constellation mapping are the same as theso-called cells in the context of the DVB standard. Then, cells areinput into a cell and time interleaver to obtain interleaved cells. Thecell interleaver interleaves within the number of cells making up acertain codeword, but no interleaving within the cells/modulationsymbols themselves occurs. In the time interleaver the number of cellsmaking up a certain codeword are interleaved with cells from a differentcodeword, but no interleaving within the cells/modulation symbolsthemselves occurs. The individual modulation symbols are expressed ascomplex numbers, where each complex number has an in-phase component orI-component and quadrature component (O-component). A pair of anI-component and a Q-component which are also called “data units” makesup a constellation symbol or cell. However, with constellation rotationand cyclic Q-delay, a cell is different from a symbol in that aQ-component of a different symbol is paired with a I-component ofanother symbol while, without the constellation rotation or a cyclicQ-delay, the paired I-component and O-component of a cell actually makeup the constellation symbol in the I/Q plan. Then, subsequent to thecell and time interleaver, the interleaved cells are forwarded to aframe builder, that produces the frames to be transmitted.

The FEC encoder performs a channel encoding. The bit interleaver isprovided for destroying statistical dependencies which would be there inthe receiver between the bits of a symbol, such as the 8 bits of a256-QAM. These statistical dependencies would have a negative impact onthe decoding of the channel codes. For example, when a 256-QAM-symbolwould be heavily distorted, then 8 sequential bits would benon-decodable, and such a so-called burst error would result in a morenegative impact when compared to a situation where the bit interleavingis applied.

The constellation is obtained, as discussed before, by a mapping of thecodebits to a certain desired signal constellation such as 16-QAM.

The constellation rotation and cyclic Q-delay is optional. However, thefollowing example clarifies the technology behind the cyclic Q-delay asdescribed in the prior art reference mentioned before.

[Before any Cyclic Delay]

Cell1 I1Q1 Cell2 I2Q2 Cell3 I3Q3 Cell4 I4Q4

[After Cyclic Delay of Length=4]

Cell1 I2Q1 Cell2 I3Q2 Cell3 I4Q3 Cell4 I1Q4

The cell interleaver makes sure that the I and Q coordinates of a symbolare transmitted at different time instants and on different subcarriersof, for example, an OFDM signal (OFDM=orthogonal frequency divisionmultiplex).

The time interleaver distributes the cells, which belong to an FECcodeword, over a certain time which is also called the interleaver timeperiod. This provides time diversity. Time diversity is advantageous inthat only a portion of an FEC codeword is strongly distorted when thetransmission channel is not so good at a certain time instant. However,the remaining less distorted portion of the codeword might be sufficientfor a successful decoding operation.

The frame builder builds the transmission frames, where a transmissionframe defines the actual transmission signal for a predetermined timeinterval such as 200 ms. Since the T2 standard allows several physicallayer pipes (PLPs), i.e. more parallel structures, but with individualmodcods, the frame builder builds the frames from different outputsignals of several existing time interleavers. Such an individualprocessing chain is also called a “pipe” in the DVB context.

On the receiver side, the chain is processed in the reverse order. Oneof the blocks in the receiver is the time de-interleaver. The timede-interleaver operates in a cell-wise manner, wherein a cell cancomprise, e.g., a received non-rotated QPSK or a rotated 256-QAM. Arotated 256-QAM has 256 possible values for the I-coordinate andadditionally for the O-coordinate. This means that a cell can havevalues such as a (transmitted in a noisy channel) 256*256-QAM=65 k-QAM,where, by contrast to a conventional 65 k-QAM, the constellation pointgrid is non-regular. Since a cell can be any one of theseconstellations, it is necessary to finely quantize the I- andO-coordinates in the receiver before the I- and Q-coordinates are inputinto the time de-interleaver. In the DVB-T2-implementation guidelines:“Digital Video Broadcasting (DVB); Implementation guidelines for asecond generation digital terrestrial television broadcasting system(DVB-T2)”, ETSI TR 102 831, it is outlined that one should apply a10-bit quantization for the l- and Q-components and one should alsoprovide several additional bits for the channel state information, i.e.for the information on an estimated signal-to-noise ratio (SNR) for thiscell so that, in the end, one will necessitate 24 to 30 bits per cell,where a cell comprises a pair of data units, i.e. an I portion as afirst data unit, a Q portion as the second data unit and the channelstate information bits.

Subsequently, reference is made to FIG. 11 illustrating a certainportion of a DVB-T2-transmitter. The transmitter comprises an FECencoder 1100. The output of the FEC encoder 1100 is connected to aninput of a bit interleaver 1101. The FEC encoder 1100 receives, as aninput, an information word which has, for example, 8100 bits and,provided that the FEC encoder 1100 applies an FEC code rate of 0.5, thenumber of code bits for an encoded information word or FEC codeword is16,200 bits. This situation is illustrated schematically in FIG. 10where item 1000 illustrates an information word and item 1001illustrates an FEC codeword. The bit interleaver 1101 performs a bitinterleaving within the bits of a single codeword and makes sure thatbits of a codeword are not distributed into other codewords and viceversa. However, the bit order of the FEC encoder output is changed inorder to increase the robustness for certain transmission conditions.The bit interleaver 1101 outputs code bits which are then input into amapper performing a constellation mapping 1102. The mapping is, forexample, a QPSK mapping where two bits are mapped into a singleconstellation symbol, so that the output of the constellation mapper1102 is a group of 8100 symbols for the embodiment as illustrated at1002 in FIG. 10. Then, the prior art provides for a constellationrotation, and cyclic Q delay operation in block 1103. The output ofblock 1103 is named a group of cells, where a cell consists of an Icomponent and a Q component, but due to the cyclic Q delay, the Qcomponent in a cell is different from the Q component which actuallybelongs to the I component in the cell as determined by theconstellation mapper and as has been discussed before. This output ofthe cyclic Q delay is input to the cell interleaver in block 1104, whereeach input element consists of a first component or I component and asecond component or Q component. When, block 1103 is not used, then amapped constellation symbol is input into the cell interleaver in block1104. The output of the cell interleaver becomes the input of the timeinterleaver 1105. The time interleaver 1105 finally outputs interleavedcells which are grouped into interleaving units and the interleavingunits are supplied to a frame builder 1106 which then builds up thetransmission frames.

The block constellation rotation and cyclic Q delay 1103 in FIG. 11 canbe optional. Therefore, the input into the cell interleaver 1104 andtime interleaver 1105 can be one of the following:

In a first possibility, the cells are normal signal constellations ormapped symbols and in the alternative possibility, the cells are rotatedco-ordinate interleaved constellations which are rotated cellsadditionally including a cyclic delay as discussed before.

As already described in Jonathon Stott, “Rotated Constellations”, thecyclic Q delay and the cell interleaver ensure that the I- and Qcomponent of a rotated (QAM-) symbol are transmitted at different timesand/or different frequencies (i.e., different sub-carriers of an OFDMsymbol). This is visualized in FIGS. 3A-3C. FIG. 3A illustrates a frameseparated into different frequency sub-carriers, where an I componentand a Q component are positioned at different frequency sub-carriers,but within the same time frame. FIG. 3B illustrates the situation wherea time-interleaving has taken place and the I component and the Qcomponent of one mapped symbol are transmitted in the same frequencysub-carriers, but at different time instants, i.e., in different frames.Finally, FIG. 3C illustrates the situation where the I component and theQ component of one and the same mapped symbol are transmitted atdifferent times and different frequency sub-carriers.

The benefit of this is that the I- and O-components of a rotated (QAM-)symbol are attenuated differently in a time- and/or frequency-selectivechannel (i.e. a fading and dispersive multi-path channel like a TypicalUrban channel with 6 paths—TU6). Hence one can achieve diversity withina (QAM-) symbol, which is not possible for conventional modulation (i.e.without constellation rotation and co-ordinate interleaving). Note thatco-ordinate interleaving is realized in DVB-T2 by the Cyclic Q Delay andthe Cell Interleaver.

FIGS. 4A-4F show this diversity effect exemplarily for a rotated QPSKconstellation. The left-hand side shows a non-rotated constellation,where the I and Q components are necessarily attenuated in the same way.The right-hand side shows a rotated constellation after co-ordinateinterleaving in the transmitter, individual fading of the I- andQ-components in the channel, and co-ordinate de-interleaving in thereceiver. This is hence the received constellation before de-rotationand demapping. For this example, one may assume that only the Icomponent undergoes fading, while the Q component is not attenuated.FIGS. 4A and 4B show the received constellations in the case of nofading. It is clear that both constellations provide the same capacity,such that constellation rotation and co-ordinate interleaving bringsneither gain nor loss.

FIGS. 4C and 4D show the case, where either the complete constellation(or only its I component, respectively) is attenuated by 6 dB, i.e. theamplitude is halved. While there is a significant performance loss forthe non-rotated case, as all Euclidian distances have been halved, theloss is lower in the rotated case. To be fair, one may not compare FIG.4C immediately with FIG. 4D; in the former, both I and Q have undergonefading, while in the latter, it is only the I component; hence for FIG.4D the channel appears to be much more favorable.

A fair comparison would be to consider two QPSK symbols, i.e. 2 I- and 2Q-components. It is assumed that one cell, i.e. one I- and oneQ-component, is affected by fading. For the non-rotated case, theattenuated I- and O-components are, of course, in the same mappedsymbol, i.e. one has one attenuated symbol like in FIG. 4C and the othernon-attenuated symbol looks like FIG. 4A. In the rotated case, one willhave two mapped symbols like in FIG. 4D, where either only the I- oronly the Q-component is attenuated.

As is commonly known, the non-rotated case with two differentlyattenuated symbols achieves only a smaller channel capacity than therotated case with two similarly affected symbols, as the latter exploitsa higher degree of diversity. The channel experienced by the rotatedscheme (here, the “channel” includes the co-ordinate interleaving andde-interleaving) appears to be more “averaged” than the one experiencedby the non-rotated scheme. As indicated by Jensen's inequality frominformation theory, an average channel has a higher capacity (for thesame averaged signal-to-noise ratio, SNR) than averaging the capacityover different channels. This is the reason, why a (e.g. Rayleigh-)fading channel of a given mean SNR necessarily has a lower capacity thanan AWGN of the same SNR.

The same principle applies here. The non-rotated case experiences onevery good channel (FIG. 4A) and one rather poor channel (FIG. 4C), whilethe rotated scheme experiences twice a medium channel (FIG. 4D). Inother words, the channel behavior has been averaged with respect to thenon-rotated case. Therefore, the resulting symbols for the non-rotatedcase (lx like in FIG. 4A and 1× like in FIG. 4C) have a lower capacitythan the corresponding symbols for the rotated case (2× like in FIG.4D).

FIGS. 4E and 4F show the constellations for a very strongattenuation >10 dB. We see from FIG. 4E that the non-rotated symbol ispractically useless, when the attenuation is strong, while the “half-wayattenuated” rotated symbol merely degenerates to a kind of 4-ASK(Amplitude Shift Keying) constellation, which can be demapped quitewell.

The conclusion is therefore that the co-ordinate interleaving, realizedby the Cyclic Q delay and the Cell Interleaver in DVB-T2, increases thediversity order, thus averages the channel experienced by the rotatedsymbol (from mapper to demapper) and thus increases the channel capacitycompared to the case of conventional non-rotated constellations.

Subsequently, the realization of the cyclic Q delay in DVB-T2 isdiscussed.

In DVB-T2, the Q components of all (QAM-) symbols belonging to a singleFEC block (i.e. codeword) are shifted by 1 symbol with respect to theirassociated I component. That is, if the FEC block contains the followingrotated symbols before the cyclic Q delay:

$\begin{matrix}\left( {I_{0},Q_{0}} \right) \\\left( {I_{1},Q_{1}} \right) \\\left( {I_{2},Q_{2}} \right) \\\ldots \\{\left( {I_{N - 1},Q_{N - 1}} \right),}\end{matrix}$

where N is the number of symbols in the FEC block, then it will be thefollowing so-called cells after the cyclic Q delay:

$\begin{matrix}\left( {I_{0},Q_{N - 1}} \right) \\\left( {I_{1},Q_{0}} \right) \\\left( {I_{2},Q_{1}} \right) \\\ldots \\{\left( {I_{N - 1},Q_{N - 2}} \right).}\end{matrix}$

The DVB-T2 standard states that the Cell Interleaver is a pseudo-randominterleaver, which mixes up all the cells of a FEC block arbitrarily.

When the time interleaver is configured to provide interleaving overframe boundaries, then it divides a FEC block into several packets (letus refer to them as Interleaver Units (IUs) in the sequel). For timeinterleaving over M T2/NGH frames (each is, e.g., 200 ms long), thecells of the FEC block (as output by the Cell Interleaver) have to bepartitioned into M IUs. These can have identical sizes, quasi-identicalsizes (i.e. sizes differ at most by 1 due to rounding effects, becausethe FEC block length is not an integer multiple of M) or individualsizes.

Then the transmitter transmits one IU per frame, i.e. the M IUs (packetsof cells) of one FEC block are transmitted in M (possibly subsequent)T2/NGH frames. An IU is hence a packet of cells, which (a) belong to thesame FEC block and (b) are transmitted in the same T2/NGH frame.

Subsequently, the disadvantages of this approach are discussed withreference to FIGS. 5A-5C.

With the current T2 standard, the chain of Cyclic Q Delay, CellInterleaver and Time Interleaver achieves a pseudo-random distributionof the I- and O-components of the rotated symbols composing one FECblock over the M T2 frames of the time interleaver duration. This leadsto a situation as displayed in FIGS. 5A-5C. The time interleaver in thisexample is M=6 T2 frames long.

In FIG. 5A, the position of the I- and Q-components of various rotatedsymbols are displayed using the same indexing. For instance, theQ-component of the rotated symbol of index 0 is located in the topsub-carrier of frame 0, while the I-component of the same rotated symbolis located in the middle of frame 2. One can see that the pseudo-randomdistribution of the I- and O-components leads to cases, where bothcomponents of one rotated symbol are in the same frame (#2, #5), orwhere they are in different frames (all others).

Now, the frames consisting of these cells are transmitted over a time-and/or frequency-selective channel. In the example of FIG. 5B, thechannel is frequency-flat but fading in time, as can be observed for thetime-varying SNR. While frames 0, 3, 4, and 5 have quite high an SNR,frames 1 and 2 are received at poor SNR and are therefore more or lesslost.

FIG. 5C then shows, which of the I- and O-components survive this fadingchannel. One finds that rotated symbols #0, #1 and #4 have one survivingcomponent each, while #2 and #3 keep both components alive. On the otherhand, #5 is completely lost.

As one saw before, this distribution of I- and Q-components issub-optimum.

It is an objective of the present invention to provide an improvedtransmission or reception concept which has an increased robustness innon-optimum transmission conditions.

SUMMARY

According to an embodiment, a transmitter for transmitting informationmay have: a mapper for generating a plurality of mapped symbols, eachmapped symbol having a first component and a second component, one ofthe first and second components being an in-phase component and theother of the first and second components being a quadrature componentfrom a codeword; and a component interleaver for generating a pluralityof interleaving units to be transmitted in a time sequence, theplurality of interleaving units consisting of at least three differentinterleaving units, wherein an interleaving unit has a plurality ofpairs of first and second components, wherein the component interleaveris configured for assigning all first components and all secondcomponents of a codeword to the plurality of interleaving units inaccordance with an interleaving rule, so that an I component of a mappedsymbol and the Q component of the same mapped symbol are never assignedto one and the same interleaving unit, but to two different interleavingunits.

According to another embodiment, a receiver for receiving informationmay have: a receiver input stage for providing a codeword having asequence of interleaving units, the codeword having interleaved mappedsymbols, each mapped symbol having a first component and a secondcomponent, wherein one of the first and second components is an in-phasecomponent and the other of the first and second components is aquadrature component, wherein the interleaved mapped symbols areinterleaved such that all first components and all second components ofa codeword have been interleaved in accordance with an interleaving ruleso that the first component and the second component belonging to thesame mapped symbol are never assigned to one and the same interleavingunit, but are assigned to different interleaving units; a componentde-interleaver for storing the codeword and for de-interleaving inaccordance with the interleaver rule to obtain de-interleaved mappedsymbols, each mapped symbol having the first component and a secondcomponent belonging to the first component; and a decoder for decodingthe de-interleaved mapped symbols to obtain a decoded information unitrepresented by the mapped symbols.

According to another embodiment, a method of transmitting informationmay have the steps of: generating a plurality of mapped symbols, eachmapped symbol having a first component and a second component, one ofthe first and second components being an in-phase component and theother of the first and second components being a quadrature componentfrom a codeword; and generating a plurality of interleaving units to betransmitted in a time sequence, the plurality of interleaving unitshaving at least three different interleaving units, wherein aninterleaving unit has a plurality of pairs of first and secondcomponents, wherein the generating a plurality of interleaving unitscomponent interleaver assigns all first components and all secondcomponents of a codeword to the plurality of interleaving units inaccordance with an interleaving rule, so that a I component of a mappedsymbol and the Q component of the same mapped symbol are never assignedto one and the same interleaving unit, but to two different interleavingunits.

According to still another embodiment, a method of receiving informationmay have the steps of: providing a codeword having a sequence ofinterleaving units, the codeword having interleaved mapped symbols, eachmapped symbol having a first component and a second component, whereinone of the first and second components is an in-phase component and theother of the first and second components is a quadrature component,wherein the interleaved mapped symbols are interleaved such that allfirst components and all second components of a codeword have beeninterleaved in accordance with an interleaving rule so that the firstcomponent and the second component belonging to the same mapped symbolare never assigned to one and the same interleaving unit, but areassigned to different interleaving units; storing the codeword andde-interleaving in accordance with the interleaver rule to obtainde-interleaved mapped symbols, each mapped symbol having the firstcomponent and a second component belonging to the first component; anddecoding the de-interleaved mapped symbols to obtain a decodedinformation unit represented by the mapped symbols.

Another embodiment may have a computer program having a program code forperforming, when running on a computer, the above methods oftransmitting and receiving information.

The present invention is based on the finding that the situation inwhich the two components of a mapped symbol are placed in the sameinterleaving unit or transmission frame has to be avoided. Since afading situation in which the transmission channel is not good enough ata certain time results in the loss of an interleaving unit ortransmission frame, i.e., the mapped symbols which are completelyincluded within a transmission frame or interleaving unit are alsocompletely lost. Stated differently, it is to be made sure that the twocomponents of a mapped symbol, i.e., the I component and the Q componentare processed in the interleaver such that an I component of a mappedsymbol and the Q component of the same mapped symbol are never assignedto one and the same interleaving unit or transmission frame but areassigned to two different interleaving units or transmission frames.Then, even though a complete interleaving unit is lost, there is a goodchance that the other component from a mapped symbol, from which acomponent got lost due to the lost interleaving unit, will be able tosurvive. Then, even though the mapped symbol has only survived with onlyone component, this component nevertheless carries valuable informationwhich may be used in a receiver-side decoder. Stated differently, havingone component of a mapped symbol survive is much better than if bothcomponents from a mapped symbol have not survived. It has been foundthat the decoder performance is much better if many mapped symbols havesurvived with one component compared to a situation in which a number ofmapped symbols have fully survived with both components and a number ofcomponents is fully lost. Referencing to FIG. 5, this means that theprior art pseudo-random-like distribution of I- and Q components is notoptimum.

From information theoretic considerations, it is best to use as muchdiversity as possible, which leads to more channel averaging. In thiscase, more “averaging” of the channel by using co-ordinate interleavingmeans: fewer symbols have both components lost (like #5), and moresymbols have at least one surviving component. This could have beenachieved, if the I-components (or likewise the Q-components) of the #2and #5 had exchanged places. One would then have one surviving componentfor #0, #1, #2, #4 and #5 plus two surviving components for #3. Thislatter distribution would lead to a higher capacity and thus to a betterperformance, i.e. lower SNR necessitated or lower error rates.

The advantage of this invention is that such an improved temporaldistribution of the I- and Q-components of rotated symbols is obtainedby replacing the existing Cyclic Q Delay and Cell Interleaver by a newinterleaver.

The transmitter for transmitting information, therefore, providessignificant advantages due to the fact that the transmitter comprises amapper for generating a plurality of mapped symbols, each mapped symbolhaving a first component and a second component, wherein one of thefirst and second components is an in-phase component and the other ofthe first and second components is a quadrature component, from acodeword. The mapped symbols are processed by a component interleaverfor generating a plurality of interleaving units to be transmitted in atime sequence one after the other, wherein the plurality of interleavingunits consists of at least three interleaving units, and wherein aninterleaving unit comprises a plurality of pairs of the first componentand the second component, wherein the component interleaver isconfigured for assigning all first components and all second componentsof a codeword to the plurality of interleaving units in accordance withan interleaving rule so that the first component of a mapped symbol andthe second component of the same mapped symbol are never assigned to oneand the same interleaving unit, but to two different interleaving units.

In an embodiment, the interleaving rule is additionally configured sothat each favourable possibility for distributing the first and secondcomponents of the mapped symbols to the different interleaving unitsoccurs one or more times in each codeword. In a further embodiment, thecomponent interleaver is configured to assign all mapped symbols in acodeword to all different favourable possibilities for distributing thefirst and second components of the mapped symbols with a predeterminednumber of occurrences in a pseudo random or a deterministic manner andto distribute the first and second components in accordance with theassignment. The assignment and the distribution take place mapped symbolby mapped symbol, or all the mapped symbols of a codeword are assignedbefore the first and second components of the mapped symbols aredistributed.

For example for interleaving over M=3 frames, there is a total of M×M=9possibilities to distribute the I and Q component of a mapped symbol:(x, y) means that the I component is transmitted in frame x and the Qcomponent in frame y. The 9 possibilities are hence (0,0), (0,1), (0,2),(1,0), (1,1), (1,2), (2,0), (2,1), (2,2). Of these M×M possibilities,M=3 are infavourable, since I and Q end up in the same frame: (0,0),(1,1), (2,2). Therefore, there are Mx(M−1) favourable possibilities todistribute the coordinates of the mapped symbols to frames orinterleaving units, in this example we have 6 possibilities.

In a further embodiment, the first and second components are assigned sothat each favourable possibility occurs for the codeword with a quantitybeing the same for all favourable possibilities or deviating by maximum50% related to the average quantity.

A corresponding receiver such as a digital receiver is configured forreceiving information. The receiver comprises a receiver input stage forproviding a codeword having a sequence of interleaving units, thecodeword comprising interleaved mapped symbols, each mapped symbolhaving a first component and a second component, wherein the interleavedmapped symbols are interleaved such that all first components and allsecond components of a codeword have been interleaved in accordance withan interleaving rule so that the first component and the secondcomponent belonging to the same mapped symbol are never assigned to oneand the same interleaving unit. Particularly the received stream is suchthat the interleaving units of different code words are mixes with eachother.

The receiver furthermore comprises a component de-interleaver forstoring the interleaving units and for de-interleaving in accordancewith the interleaving rule to obtain the interleaved mapped symbols,each de-interleaved mapped symbol comprising a first component and asecond component belonging to the first component. The receiverfurthermore comprises a decoder for decoding the de-interleaved mappedsymbols to obtain decoded information units represented by the mappedsymbols.

Rotated constellations may be used. In this embodiment, the transmitterside comprises a constellation rotation stage and the receiver sidecomprises a constellation de-rotation stage, which is, for example, partof the decoder. Further implementations of the decoder may comprise anykind of FEC or turbo decoder or, for example, a Viterbi decoder or, ofcourse, a straightforward hard decision decoder.

BRIEF DESCRIPTION OF THE DRAWINGS

Subsequently, embodiments of the present invention will be discussed inmore detail with reference to the accompanying drawings, in which:

FIG. 1A illustrates an embodiment of a digital transmitter;

FIG. 1B illustrates details of the pre-mapper processing and the mapperof FIG. 1 a;

FIG. 1C illustrates details of the post-interleaver processing of FIG. 1a;

FIG. 2A illustrates an embodiment of a digital receiver;

FIG. 2B illustrates details of the pre-de-interleaver processing of FIG.2 a;

FIG. 2C illustrates details of the decoder for post-de-interleaverprocessing of FIG. 2 a;

FIGS. 3A-3C illustrate the combined time/frequency component diversity;

FIGS. 4A-4F illustrate details on the use of rotated constellations innon-optimum transmission channels;

FIGS. 5A-5C illustrate a situation of a prior art transmitter in thepresence of a varying channel quality;

FIGS. 6A-6C illustrate a similar situation as in FIGS. 5A-5C but with adifferent component interleaving;

FIGS. 7A-7C illustrate three different embodiments for interleaving thefirst and second components of the mapped symbols in a codeword;

FIG. 8A illustrates a time sequence of interleaving units;

FIG. 8B illustrates thirty different favourable possibilities for theexample of six interleaving units in accordance with the invention;

FIG. 8C illustrates an embodiment of performing the interleaveroperation and, with respect to the interleaving rule, a correspondingde-interleaver operation;

FIG. 8D illustrates a further embodiment of an interleaver controllerimplementation for interleaving and de-interleaving;

FIG. 8E illustrates the further interleaver controller implementationand corresponding de-interleaver implementation;

FIG. 9A illustrates details of a specific interleaver implementation;

FIG. 9B illustrates details of a certain de-interleaver implementation;

FIG. 10 illustrates the development of an information word havinginformation units such as bits until interleaving units to betransmitted sequentially in time and vice versa; and

FIG. 11 illustrates a prior art DVB-2 transmitter chain.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates a digital transmitter. The digital transmittercomprises a pre-mapper processing block 100. The output of thepre-mapper processing block 100 is a codeword which has, for example,16,200 bits as illustrated at 1001 in FIG. 10. The codeword is inputinto a mapper 102. The mapper is configured for generating a pluralityof mapped symbols such as the 8100 symbols 1002 illustrated in FIG. 10.Each mapped symbol comprises a first component and a second component,where one of the first and second components is an in-phase componentand the other of the first and second components is a quadraturecomponent. The in-phase component is also known as the I component, andthe quadrature component is also known as the Q component. When it issaid that the mapped symbols are complex symbols, then the I componentrepresents the real part of a complex value, and the Q componentrepresents the imaginary part of the complex value. The output of themapper 102, i.e., the mapped symbols 1002 illustrated in FIG. 10 areinput into a component interleaver 104 for generating a plurality ofinterleaving units, the plurality of interleaving units consisting of atleast three interleaving units. In the implementation exampleillustrated in FIG. 10, there are six interleaving units 1004, butadvantageously there are three, four, five, six or even moreinterleaving units. Each interleaving unit comprises a plurality ofpairs of a first component and a second component, but the firstcomponent and the second component comprised in a pair are not from thesame mapped symbol, i.e., do not belong together for jointlyrepresenting the complex value output by the mapper for a certain numberof bits. Instead, the first and second components are taken fromdifferent mapped symbols.

Specifically, the component interleaver 104 is configured for assigningall first components and all second components of a codeword to theplurality of interleaving units in accordance with an interleaving rule,so that a first component of an mapped symbol and the second componentof the same mapped symbol are never assigned to one and the sameinterleaving unit but are assigned to two different interleaving units.The interleaving units 1004 of FIG. 10 are output by the componentinterleaver 104 and input into a post-interleaver processing 106. Thepost-interleaver processing processes the interleaving units so thatthey are transmitted to a digital receiver such as the digital receiverillustrated in FIG. 2A.

The mapper 102 is configured for applying any constellation diagram.When, for example, the mapper has a QPSK (quadrature phase shift keying)constellation diagram, then the constellation diagram has four (complex)points, and each point is represented by two messaging units such ascode bits. This means that each state represents two bits and the mapperoutputs 8100 mapped symbols for 16,200 bits.

However, when the mapper is configured for applying a 16-QAMconstellation diagram, then each (complex) state of the constellationdiagram represents four bits and one codeword having 16,200 bits wouldresult in 4050 mapped symbols at the output of the mapper 102.

FIG. 1B illustrates details of the pre-mapper processing. In anembodiment, the pre-mapper processing 100 comprises an FEC encoder 100 aand a subsequently connected bit interleaver 100 b. The FEC encoder 100a is configured for encoding an input information word to output an FECcodeword or codeword or FEC block (FEC=forward error correction). In anembodiment, the FEC encoder may comprise a code rate of 1/2 which meansthat the codeword output by block 100 a has a number of bits which istwice the number of bits of the input information word. However, whenthe FEC encoder has a code rate of 1/4 then the number of output bits ofa codeword would be four times the number of bits in the inputinformation word and so on. Hence, the FEC encoder is configured forencoding an input information word to obtain a codeword having a numberof codeword units such as bits. The FEC encoder output is input into abit interleaver 100 b or “codeword unit interleaver” for interleavingthe codeword units within the codeword but not among two or morecodewords and the bit interleaver results in a codeword which isbit-interleaved. However, the bit interleaver is optional. When block100 b is not provided, then the input into the mapper 102 of FIG. 1A isa codeword which has not been interleaved, and when the bit interleaver100 b is present, then the codeword input into the mapper has beeninterleaved by the functionality of the bit interleaver. The bitinterleaver may be configured for implementing a straightforwardrow/column interleaver, which means that the codeword is written into amemory row after row and the output is read from the memory column aftercolumn.

FIG. 1B furthermore illustrates details of the mapper 102 of FIG. 1A.The mapper 102 may comprise a constellation mapper 102 a and asubsequently connected constellation rotation block 102 b. Depending onthe implementation, the constellation mapping and the constellationrotation in blocks 102 a, 102 b can also be applied within a singleoperation. For clarity of description, however, the mapper 102 isillustrated in FIG. 1B as two separate actions, where the first actionis a straightforward mapping in block 102 a in accordance with a certainconstellation diagram and the second action is a rotation of the mappedsymbols so that the mapped symbols become rotated mapped symbols.However, when the constellation rotation 102 b is not applied, then themapped symbols are non-rotated mapped symbols generated by block 102 aalone. It is to be noted that constellation rotation functionalitieshave a good effect together with the described component diversity,since the mapped symbols, which have been rotated, have thecharacteristic that the first component as well as the second componentcomprise information on both bits (in the example of QPSK) which meansthat the information is more distributed compared to a situation inwhich the first component would just represent the first bit of a bitpair for QPSK and the second component would just represent the secondbit of a pair for a QPSK mapped symbol.

It is to be noted that rotated constellations exist not only for QPSKbut for all other useable and well-known constellation diagrams such asQAM, 16 QAM, 8 PSK or any other kind of constellation diagrams ormapping rules.

The post-interleaver processing block 106 illustrated in FIG. 1C maycomprise a frame builder 106 a, the subsequently connected frequencyinterleaver 106 b and, finally, an RF transmitter 106 c (RF=radiofrequency). Basically, the post-interleaver processing can be consideredas a transmitter circuit for transmitting each interleaving unit at adifferent time in the time sequence in which the interleaving units areto be transmitted. However, applying a further frequency interleaving isadvantageous for frequency-fading channels so that, in the end, not onlyrobustness with respect to time-fading channels but also with respect tofrequency-fading channels is obtained. The frame builder 106 a mayfurthermore be configured to build frames not only for a singletransmitter chain illustrated in FIG. 11 but from several suchtransmitter chains illustrated in FIG. 11. In view of this, the framebuilder 1105 may be implemented in the same way as the frame builder 106a in FIG. 1C. Accordingly, when more than one transmitter chain asillustrated in FIG. 11 is presented, the combination of the framebuilder 106 a and the frequency interleaver 106 b may mix up in the timeand the frequency domain the component-wise interleaved symbols from themultiple transmitter chains, but only in such a way that all symbolsbelonging to the same interleaving unit are transmitted in the sametransmission frame.

FIG. 2A illustrates a block diagram of a digital receiver for receivinginformation. The receiver comprises a receiver input stage 201 forperforming a pre-de-interleaver processing. Specifically, the receiverinput stage 201 is configured for providing a codeword having a sequenceof interleaving units, the codeword comprising interleaved mappedsymbols, wherein each mapped symbol has a first and a second component,wherein one of the first and second components is an in-phase componentand the other one of the first and second components is a quadraturecomponent. The interleaved mapped symbols are interleaved in accordancewith the interleaving rule applied by the digital transmitter of FIG.1A. Specifically, the interleaving rule, by which the interleaved mappedsymbols have been interleaved is such that all first components and allsecond components of a codeword have been interleaved in accordance withthe interleaving rule such that the first component and the secondcomponent belonging to the same mapped symbol are never assigned to oneand the same interleaving unit or transmission frame. Hence, thereceiver input stage 201 provides an interleaved stream of mappedsymbols comprising the interleaving units separated from each other ashave been generated by the component interleaver 104 of FIG. 1A. Theinterleaved stream of mapped symbols is input into a componentde-interleaver 202. The component de-interleaver 202 is configured forstoring the codeword consisting of the interleaved stream of mappedsymbols and for de-interleaving in accordance with the interleaving ruleto obtain a de-interleaved mapped symbol, each mapped symbol comprisinga first component and a second component belonging to the firstcomponent. Hence, the output of block 202 is the plurality of mappedsymbols 1002 illustrated in FIG. 10, naturally affected by transmissionerrors, noise, etc. However, if there was a perfect transmissionchannel, then the output of the component de-interleaver 202 would beexactly the same as the mapped symbols indicated at 1002 in FIG. 10 forthe transmitter side. Hence, FIG. 10 can also be seen as arepresentation of the situation in the receiver, when FIG. 10 is readfrom bottom to top.

The de-interleaved mapped symbols are input into a decoder 204 forperforming a post-de-interleaver processing to obtain decodedinformation units which have been represented by the mapped symbols.Hence, the result of block 204 corresponds to the information word 1000consisting of the individual information units illustrated in FIG. 10.

The receiver input stage 201 of FIG. 2A comprises, as illustrated inFIG. 2B, an RF front end 201 a, a frequency-de-interleaver 201 b and aframe decomposer 201 c. The frame decomposer is configured to providestreams to different component de-interleavers simultaneously, i.e., toimplement different so-called pipes.

Hence, the pre-de-interleaver processing corresponds to thepost-interleaver processing illustrated in FIG. 1C. However, when thepost-interleaver processing of FIG. 1C is implemented in a differentmanner, i.e., when a frequency interleaver 106 b is not provided forexample or provided at a different position in the transmitter chain,then the pre-de-interleaver processing is configured analogously so thatthe actions performed on the encoder side are undone or cancelled bycorresponding operations on the decoder or receiver side.

FIG. 2C furthermore comprises a further implementation of the decoder204 for post-de-interleaver processing. The decoder comprises aconstellation de-rotation block 204 a, a de-mapper 204 b and asubsequently connected information decoder 204 c. However, as is knownin the art, a large variety of decoding operations exist where thedemapper and the information decoder are included in one and the samefunctionality. Such decoding concepts comprise MLSE or other decodingconcepts such as iterative decoding and demapping concepts relying onsoft input/soft output data for finally obtaining the decodedinformation units.

FIGS. 6A-6C illustrate one approach, in which the interleaving isperformed in such a way that all first components and all secondcomponents of an information word are assigned to two differentinterleaving units. In this approach, the algorithm known from thecyclic Q delay indicated in FIG. 11 is used but the Q component of anyrotated symbol is shifted by one interleaving unit instead of onesymbol.

In other words: the Q-component of any rotated symbol is transmitted ina frame after its corresponding I-component. For the very last frame,that the considered FEC block occupies inside the time interleaver, theO-component is transmitted in the very first frame inside the timeinterleaver (i.e. the IU-wise shift is cyclic over the time interleaverlength). Let us refer to this scheme as “Cyclic IU Delay”.

FIG. 6A shows this for an example: #0, #1 and #2 all have theirI-component in frame 0 and their O-component in frame 1. #3 has itsI-component in frame 1 and its Q-component in frame 2. #4 has itsI-component in frame 2 and its Q-component in frame 3. #5 has itsI-component in frame 4 and its O-component in frame 5. Finally, #6 hasits I-component in frame 5, and its O-component in frame 0 (i.e. thecyclic shift described above).

Transmitting this temporal distribution of I- and Q-components over thesame fading channel as in the previous example (FIG. 4B) leads to thechannel output displayed in FIG. 6C. We find that #0, #1, #2 and #4 haveone surviving component, and #5 and #6 have two surviving components.

On the other hand, #3 is completely lost. The same is true for allrotated symbols, which have their I-component in frame 1 and accordinglytheir Q-component in frame 2.

This embodiment can be improved as described subsequently, and thesubsequently described algorithms provide maximum time diversity underall circumstances.

To explain this embodiment, we introduce an ordered pair (m; k) for eachsymbol: m expresses the index of the interleaving unit that carries theI-component of this symbol, while k represents the index of theinterleaving unit that carries the Q-component of this symbol.

For maximum diversity, the I- and O-components of the rotated symbolsshould use as many ordered pairs (m; k) as possible except those, wherem and k are identical: (m; k=m). Hence, for a time interleaver of lengthM frames, there are M*(M−1) such suitable pairs with m unequal k. Thenew Component Interleaver can assign all rotated symbols on apseudo-random basis to these pairs, and then distribute their I- andQ-components accordingly to the respective IUs, that is frames, i.e. theI-component to IU/frame k and the O-component to IU/frame m. If weconsider the example of FIG. 4 b with M=6 and the given fading channel,we have a loss of both components only for symbols associated with the 2pairs (1; 2) and (2; 1) out of 6*(6-1)=30 suitable pairs, i.e. only for1/15 of all symbols. Hence, we have achieved maximum diversity, i.e.maximum averaging by this method.

This algorithm is described in more detail with respect to FIGS. 8A-8C.FIG. 8A illustrates a sequence of interleaving units corresponding tothe interleaving units 1004 of FIG. 10, when the interleaving units aretransmitted in the time sequence. FIG. 8A is only exemplary and,typically, the interleaving units would not be transmitted with a breakbetween the interleaving units, but time-contiguous to each other, i.e.,without any substantial breaks in between. However, when there are, forexample, other interleaving units from other transmitter chains or,generally, other audio or video programs, then there could beinterleaving units from other channels interspersed between theinterleaving units IU1 to IU6 illustrated in FIG. 1A. In thisembodiment, six interleaving units are indicated.

The table in FIG. 8B illustrates all thirty possible ordered pairs as tohow an mapped symbol could be distributed among the interleaving units.Exemplarily, the notation 2,5 means that the first or I component of anmapped symbol is assigned to interleaving unit 2 and the second or Qcomponent of the same mapped symbol is assigned to interleaving unit 5.Analogously, the notation 5,1, for example, means that the I componentof a mapped symbol is assigned to the fifth interleaving unit and thesecond or Q component is assigned to the first interleaving unit and soon. As illustrated in FIG. 8C at 801, a determination is made for eachmapped symbol included in the codeword output by the mapper 102 of FIG.1A according to which possibility for the ordered pairs this mappedsymbol is to be distributed. Hence, all the 8100 symbols, for example,are assigned to the different (thirty) possible ordered pairs indicatedin the table 800 of FIG. 8B. The determination of the ordered pair foreach mapped symbol of step 801 may be performed in such a way that eachpossible ordered pair receives almost the same number of mapped symbols.Hence, this interleaving rule makes sure that a situation cannot occurin which one and the same mapped symbol has both of its componentswithin the same interleaving unit, since these six ordered pairs whichare forbidden, i.e., where both components would be assigned to one andthe same interleaving unit, do not and are not allowed to occur in thetable 800.

Subsequent to the determination of the ordered pair to be taken for eachmapped symbol in step 801, the step 802 is performed in which the Icomponent and the Q component of the mapped symbols are distributed inaccordance with the ordered pair determined in step 801. A first way toimplement steps 801 and 802 would be to perform an assignment for eachof the mapped symbols for a codeword before the actual distribution isperformed and, subsequent to the determination for all mapped symbols ina codeword, the actual distribution into the interleaving units isperformed. However, it is of advantage to perform the determination ofthe ordered pair for a certain mapped symbol and to then distribute theI and Q components of this mapped symbol into the correspondinginterleaving unit and to subsequently perform both steps for the nextmapped symbol and so on.

In a further alternative, the Q components are obtained in a certainorder, and the Q components are resorted in accordance with a specifiedrule, such as by cyclically shifting within a row. The I componentswould not be interleaved at all and one would not have to specify anyordered pairs at all, but the result would nevertheless be the situationillustrated in FIG. 7A, table 1, i.e., items 701 a and 701 b.

The way in which the determination of the favourable distributionpossibility for each mapped symbol is performed can be done in a pseudorandom or a systematic way, which means that this interleaving rule canbe reversed at a de-interleaver included in a receiver which thenapplies the corresponding interleaving rule so that the distribution iscancelled out. It is to be noted that the pseudo-random distributionaccording the present invention differs from the pseudo-randomdistribution in the DVB-T2 standard in a very significant point: Whereasthe latter distributes over all M² possible ordered pairs, the deviceaccording to this invention employs only the Mx(M−1) favourablepossibilities, where I and Q component are distributed to differentinterleaving units, i.e. frames. One way of performing this systematicprocedure is to use the table 800 and to start with the first mappedsymbol and to use for the first mapped symbol the first element such as1,2 in table 800 and to then use the second mapped symbol and to applythe second value of the table which is 2,1 and so on. Then, the numberof mapped symbols is “walked through” and the table 800 is walkedthrough from left to right and row by row, so that, for example, thesixth mapped symbol receives a distribution 6,1 and the seventh mappedsymbol receives a distribution 1,3 and so on. Based on table 800 whichrepresents an interleaving rule in this case, a correspondingde-interleaver processing can easily be performed by just reversing thesorting done in the transmitter-side interleaver. However, analternative procedure would be that the table 800 is walked throughcolumn-wise so that the second mapped symbol receives 1,3 as thedistribution possibility, the fifth mapped symbol receives 1,6 and thesixth mapped symbol receives 2,1 as the distribution possibility.

It is clear that many other “pseudo random” procedures can be performedsuch as walking through the table 800 in a different manner such as byrows but where from one distribution possibility to the next a certainnumber of intermediate possibilities are left out and are filled outlater. For example, one way would be to use for the first mapped symbolthe possibility 1,2 and to use for the second mapped symbol thepossibility 3,1 and to use for the third mapped symbol the possibility5,1 and to use for the fourth mapped symbol the possibility 2,1 and touse for the next mapped symbol the possibility 4,1 and so on.

Subsequently, reference is made to FIGS. 7A-7C illustrating threedifferent tables, where each table has an I component table and a Qcomponent table. In the table 1 embodiment, the I- and Q componenttables 701 a and 701 b are indicated. The tables are to be read so thatthe first pair in interleaving unit 0 (IU0) would be the I component ofmapped symbol 0 and the Q component of mapped symbol 500. Exemplarily,the second pair in interleaving unit 4 would comprise the I component ofmapped symbol 401 and the Q component of mapped symbol 201. In thisembodiment, the distribution is systematic instead of pseudo-random.Here, the I-components of a FEC block are contiguously partitioned intothe IUs 0 to M−1, when the interleaver has length M frames, see theexample shown in Table 1. In this example, M=6 and there are 100I-components per IU, i.e. 6001-components (or symbols) per FEC block.One may observe that each IU is transmitted in a different frame, asmentioned before. The shading in the table represents the IU index,which carries the 1-component of a symbol (e.g. dark for symbols 0, 1, 2etc., because all their I-components are carried in IU 0). Now theQ-components are assigned to these IUs in a different manner.

While I0, the I-component of symbol 0, is in IU 0, the correspondingQ-component Q0 is in IU 1. I1, I2, I3, and I4 are all in IU 0, but theircorresponding Q components Q1, Q2, Q3, and Q4 are in IU 2, IU 3, IU 4,and IU 5, resp. Next comes I5, which again is in IU 0. Now, thecorresponding Q5 is in IU 1—just as Q0 is. Hence, the assignment patternfrom Q0 to Q4 is cyclically repeated every 5 symbols for the first 100symbols, whose O-component is located in IU 0.

A similar pattern, just cyclically shifted by one IU (one column), isused for symbols 100 to 199. This pattern is repeated in cyclicallyshifted versions for all other symbols of the FEC block, such that thepicture of Table 1 appears.

Subsequently, a further embodiment is illustrated with respect to table2 comprising an I component table 702 a and a Q component table 702 b.The notation is the same as discussed previously, i.e., that, forexample, the first pair in IU0 would consist of the I component ofmapped symbol 0 and the Q component of mapped symbol 500. The secondpair in interleaving unit 0 would consist of the I component of mappedsymbol 1 and the Q component of mapped symbol 501.

In FIG. 7B, items 702 a, 702 b, two consecutive symbols use the sameassignment of their I- and Q-components to the IUs. Hence, not onlysymbol 0 has its I-component in IU 0 and its Q-component in IU 1, butthe same assignment is used for symbol 1. Then the assigned IU for theO-component is cyclically shifted for the following symbols 2, 3, thenfor 4, 5 etc. until 99, similarly to the above example. For symbols 100to 199, 200 to 299 etc., a cyclic shift of this assignment pattern byone IU is used.

Of course, this assignment pattern could be extended to have the sameassignment to three, four etc. consecutive symbols instead of two.

FIG. 7C illustrates a further embodiment in connection with the Icomponent table 703 a and the Q component table 703 b. However, thelogic behind the table 3 embodiment is substantially different from thelogic behind the table 1 and table 2 embodiments. Table 3 illustratesthe first 42 symbols of an FEC block or codeword, indexed from 0 to 41.

The I-component is sequentially assigned to the IUs, i.e. symbol 0 to IU0, symbol 1 to IU 1 etc. Then the O-components are assigned in the showncyclic manner, which ensures that never I- and O-component are in thesame IU. This procedure can be implemented by a shift register for the Icomponents, which delays the I components by a specified number ofsymbols such as 6 symbols. The Q components are loaded in a furtherregister, which is configured to implement an internal resorting afterhaving received the specified number of Q components, such as sixcomponents. The internal resorting takes place in accordance with FIG.7B, item 703 b. Then the register is controlled to output the specifiednumber (such as 6) Q components sequentially (together with the delayedI components). A further device distributes these cells one after theother to the specified number (such as 6) of interleaving units.

Note that the number of symbols associated with an ordered pair (k; m),where the symbol's I-component is in IU k and the O-component is in IUm, is not necessarily the same for all pairs (k; m). This depends on thenumber of symbols in a FEC block. E.g. if a FEC block contains only the42 symbols shown in Table 3, then there are two symbols for the pair (0;1), namely the one indexed by 0 and the one with 30, while there is onlyone symbol for (0; 4), namely index 18. Only if the FEC block length isa multiple of M*(M−1), this number is the same for all pairs (k; m).Otherwise, the number is “almost” constant, i.e. it varies by at most 1.

FIG. 8D illustrates a mathematical implementation of the cyclic Q delayillustrated in FIG. 7C, items 703 a and 703 b. In this interleavercontroller implementation, which is mathematically expressed in FIG. 8D,the mapped symbol index is j and the number of the interleaving unit, inwhich the I component of this mapped symbol is to be placed iscalculated by evaluating j mod M where M is the number of interleavingunits.

Correspondingly, the Q component of this mapped symbol is distributedinto an interleaver unit which is calculated by evaluating theexpression 805 in FIG. 8D, where the function “floor” stands for “takingthe lower nearest integer”. Hence, the value “floor” of 6.1 or 6.9 wouldboth be equal to 6.

FIG. 8E illustrates the functionality of FIG. 8D in an interleaver-likedescription. Again, the I component of the symbol j is to be interleavedor placed into a cell with an index to be calculated by evaluatingexpression 806. Similarly, the Q component of the symbol is to beinterleaved into the cell with the cell to be determined by evaluatingthe expression 807 in FIG. 8E. The distribution of the cells into theinterleaving units is indicated in item 808 of FIG. 8E. Hence, the cellsrepresent all places for pairs of I and Q components throughout allinterleaving units and, subsequent to the placement of the I and Qcomponents in the cells or “pairs” of I and Q components within aninterleaving unit, a further placement from the cells into theinterleaving units takes place in accordance with the expression 808.Hence, the implementation in FIG. 8D can be seen as a direct translationof I and Q components into interleaving units and the implementation ofFIG. 8E can be seen as a kind of an “indirect” implementation, where thecell index is first calculated and subsequently, the cells are placedinto interleaving units.

The de-interleaver description that corresponds to the interleaverdescription of FIG. 8D or 8E are as follows.

With respect to the description in FIG. 8D, the following applies forthe matching de-interleaver:

Sequentially take 1 cell from received IU 0, 1 cell from received IU 1,etc. This gives cells 0 to FEC block length −1. For each cell m: Icomponent of received cell m is de-interleaved to column m mod M, Qcomponent of received cell m is de-interleaved to column (m+M−1−floor(m/M) mod (M−1)) mod M.

After the de-interleaving, the de-interleaved cells of the FEC block areread row-by-row, i.e. 1 cell from column 0, 1 cell from column 1, etc.

With respect to the description in FIG. 8E, the following applies forthe matching de-interleaver, i.e. the de-interleaver description wouldbe based on:

de-interleave the I component of cell n to the symbol with index floor(n/N)+(n mod N)*M, where N=FEC block length/M

de-interleave the Q component of cell n to the symbol with index (floor(n/N)+M−1−(n mod N) mod(M−1)) mod M+(n mod N)*M,

where the IU k, with k from 0 to M−1, is composed of the cells withindices N*k+0 to N*k+(N−1). The de-interleaved symbols are output in theorder of their index.

When the present invention is compared to the prior art illustrated inFIG. 11, it becomes clear that this new component interleaver orcomponent de-interleaver replaces the combination of cyclic Q delay andcell interleaver, such that any extra cell interleaver is not requiredany more.

The implementation illustrated in the context of items 703 a, 703 b inFIG. 7C and illustrated in the context of FIG. 8D or 8E has a furthersignificant advantage. The advantage is that this procedure allows thereceiver to read larger bursts from an (external) memory (like IUs)without requiring an extra memory for all the cells of an FEC block. Theprior art interleaver as well as implementations in accordance withTable 1, Table 2 need this extra memory because the receiver is to storethe symbols of an FEC block after reversing the component interleavingand before feeding the symbols to the constellation de-rotation, thede-mapper, the bit de-interleaver, and the FEC decoder. In the FIGS. 8Dand 8E embodiments, which is graphically illustrated at 703 a and 703 bin FIG. 7C, it is sufficient to load only the first parts of IUs 0-5 inorder to reverse the component interleaving and feed these symbols tothe demapper and bit de-interleaver, and it is not necessary to load thecomplete interleaving units 0-5. Exemplarily, a read unit of ade-interleaver could load the first five cells from each interleavingunit, i.e., the read unit discussed later on with respect to FIG. 9Bwould apply six bursts of five cells each, and then reverse thecomponent interleaver. Then, these first 30 symbols would be forwardedto the de-rotation, demapping and bit de-interleaving block.

This approach is quite sufficient with respect to memory accesses (readonly bursts from an external memory, not individual cells), but itnecessitates only an extra memory of six times five cells for bufferingthese read bursts. Naturally, the burst size could be any number such as16 instead of five cells.

FIGS. 9A and 9B illustrate a specific implementation of an interleaverin accordance with the present invention or a de-interleaver inaccordance with the present invention. The interleaver comprises a writeunit 900, a subsequently connected memory 901, which is the interleavermemory, and which can be implemented as an external random access memory(RAM), when the digital transmitter is implemented in a hardwired orsemi-hardwired integrated circuit. The integrated circuit will thencomprise the write unit 900 and a read unit 902 together with aninterleaver controller 903. The interleaver controller 903 applies oneof the exemplarily illustrated interleaving rules to the read unit 902,and the read unit 902 reads the memory 901, which has been provided withthe mapped symbols in a certain order, so that the interleaved sequenceof interleaving units output by the read unit 902 corresponds to theinterleaver rule controlled by the interleaver controller 903. When, forexample, the embodiment in Table 1, items 701 a, 701 b is considered,the implementation of the I component interleaving would be so that thewrite unit, for example, writes into the interleaver memory in arow-wise manner and there would be, for example, 100 columns and sixrows. Then, the read unit 902 would read out the first row of the memoryin order to obtain the I components of the first 100 mapped symbols forthe first interleaving unit IU0 and, specifically, for the firstcomponents for interleaving unit 0. Then, the read unit would read thesecond row for obtaining the I components for the second interleavingunit IU 1, etc. Then, the read unit would read from the interleavermemory 901 in the order dictated by the first column of item 701 b inFIG. 7A. The read unit would read from the memory where mapped symbol500 is written. Then, the read unit would read from the memory whereinformation unit 401 is placed. Then, the read unit would read from thememory where information unit 302 is placed, etc.

FIG. 9B illustrates a corresponding interleaver which, again, comprisesa write unit 910, a de-interleaver memory such as an external RAM 912, aread unit 914, a de-interleaver controller 916 and an internal buffer918 within the read unit 914. As in the FIG. 9A implementation, the readunit 914 includes the internal buffer 918 and the de-interleavercontroller 916 may be part of an integrated circuit which is fullyhardwired or semi-hardwired, while the de-interleaver memory 912 wouldbe implemented as an external RAM. Now, when the FIG. 7C Table 3embodiment is considered, it becomes clear that the read unit 914 canadvantageously perform a row-wise burst readout. This is due to the factthat the tables in FIGS. 7A-7C illustrate the situation of thede-interleaver memory 912, when the interleaved data of a codeword hasbeen received and written into the memory. Then, the memory would have,for example, six columns and, for example, 100 rows for the exemplaryimplementation as cited in FIGS. 7A-7C. Each place in the memory wouldbe so that it can store an I component and a Q component. Then, the readunit 940 would simply read the first row of the memory and wouldreceive, from this first row of the memory, all I and Q components forthe first five mapped symbols. Then, these five mapped symbols simplycan be forwarded to the de-rotation procedure and the internal memory918 only has to store these five I components and the corresponding fiveQ components. The same is true for all the other rows, and, therefore,any intermediate storage apart from storing the I and Q components of arow is not required. Such a situation, however, would be necessitatedwhen the embodiments of Table 1 and Table 2 are implemented and areread. It becomes clear from the Table 702 a and 702 b that a row-wiseread operation from the memory does not result in consecutive mappedsymbols to be further processed. Instead, if, for example, Table 2 isconsidered, it becomes clear that the first row-wise read operationresults in mapped symbol 500 and mapped symbol 0 and a useful furtherprocessing of these mapped symbols is only possible when theintermediate information units 1-499 have also been de-interleaved.Hence, the internal buffer 918 can be made considerably small for theFIG. 7C items 703 a, 703 b embodiment.

In other words, embodiments of the present invention can be consideredto comprise, on the sender side a component interleaver, which receives,as an input, (rotated) symbols of an FEC block and which provides, at anoutput, several interleaving units, which consist of cells, which areformed of I and Q components of the (rotated) symbols of an FEC blocksuch that (a) the number of symbols, whose I components are interleavedto IU k and whose Q components are interleaved to IU n, are different byat most one for all pairs (k;m) with k not equal m, and where (b) the Icomponent of a symbol is never interleaved to the same interleaving unitas the Q component of this symbol. In an embodiment, this procedure isperformed together with rotated constellations, so that the symbols arerotated symbols.

In a further embodiment, this procedure is performed in the context of atime interleaver, so that the cells of a IU are transmitted close toeach other with respect to time, while different IUs are transmittedseparated from each other in time and one after the other.

In a further implementation, the assignment from the components of themapped symbols to the interleaving units is based on a pseudo-randomprinciple, where only favourable possibilities for distributing the Iand Q components are employed.

In a further embodiment, the assignment is formed based on the procedureillustrated in the context of items 701 a, 701 b of FIG. 7A.

In a further embodiment, the assignment is performed based on theembodiment illustrated in the context of items 702 a, 702 d of FIG. 7B.In a further embodiment, the assignment is performed based on theimplementation disclosed in the context of items 703 a, 703 b of FIG.7C.

In a further embodiment, the assignment is performed based on theimplementation in FIG. 8B or 8E.

The receiver is implemented correspondingly, where the receiver mirrorsthe corresponding transmitter implementation.

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding block or item or feature of a correspondingapparatus.

Depending on certain implementation requirements, embodiments of theinvention can be implemented in hardware or in software. Theimplementation can be performed using a digital storage medium, forexample a floppy disk, a DVD, a CD, a ROM, a PROM, an EPROM, an EEPROMor a FLASH memory, having electronically readable control signals storedthereon, which cooperate (or are capable of cooperating) with aprogrammable computer system such that the respective method isperformed.

Some embodiments according to the invention comprise a non-transitorydata carrier having electronically readable control signals, which arecapable of cooperating with a programmable computer system, such thatone of the methods described herein is performed.

Generally, embodiments of the present invention can be implemented as acomputer program product with a program code, the program code beingoperative for performing one of the methods when the computer programproduct runs on a computer. The program code may for example be storedon a machine readable carrier.

Other embodiments comprise the computer program for performing one ofthe methods described herein, stored on a machine readable carrier.

In other words, an embodiment of the inventive method is, therefore, acomputer program having a program code for performing one of the methodsdescribed herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a datacarrier (or a digital storage medium, or a computer-readable medium)comprising, recorded thereon, the computer program for performing one ofthe methods described herein.

A further embodiment of the inventive method is, therefore, a datastream or a sequence of signals representing the computer program forperforming one of the methods described herein. The data stream or thesequence of signals may for example be configured to be transferred viaa data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example acomputer, or a programmable logic device, configured to or adapted toperform one of the methods described herein.

A further embodiment comprises a computer having installed thereon thecomputer program for performing one of the methods described herein.

In some embodiments, a programmable logic device (for example a fieldprogrammable gate array) may be used to perform some or all of thefunctionalities of the methods described herein. In some embodiments, afield programmable gate array may cooperate with a microprocessor inorder to perform one of the methods described herein. Generally, themethods may be performed by any hardware apparatus.

While this invention has been described in terms of several embodiments,there are alterations, permutations, and equivalents which will beapparent to others skilled in the art and which fall within the scope ofthis invention. It should also be noted that there are many alternativeways of implementing the methods and compositions of the presentinvention. It is therefore intended that the following appended claimsbe interpreted as including all such alterations, permutations, andequivalents as fall within the true spirit and scope of the presentinvention.

1. A transmitter for transmitting information, comprising: a mapper forgenerating a plurality of mapped symbols, each mapped symbol comprisinga first component and a second component, one of the first and secondcomponents being an in-phase component and the other of the first andsecond components being a quadrature component from a codeword; and acomponent interleaver for generating a plurality of interleaving unitsto be transmitted in a time sequence, the plurality of interleavingunits comprising at least three different interleaving units, wherein aninterleaving unit comprises a plurality of pairs of first and secondcomponents, wherein the component interleaver is configured forassigning all first components and all second components of a codewordto the plurality of interleaving units in accordance with aninterleaving rule, so that an I component of a mapped symbol and the Qcomponent of the same mapped symbol are never assigned to one and thesame interleaving unit, but to two different interleaving units.
 2. Thetransmitter in accordance with claim 1, wherein the componentinterleaver is configured so that the interleaving rule is implementedsuch that each favourable possibility, where the first and secondcomponents of the mapped symbols are distributed to differentinterleaving units occurs and do not end up in the same interleavingunit, for a codeword, one or more times.
 3. The transmitter inaccordance with claim 1, wherein the component interleaver is configuredto assign all mapped symbols in a codeword to all different favourablepossibilities, where the first and second components of the mappedsymbols are distributed to different interleaving units occurs and donot end up in the same interleaving unit, for distributing the first andsecond components of the mapped symbols to the interleaving units with apredetermined number of occurrences in a pseudo-random or deterministicmanner and to distribute the first and second components in accordancewith the assignment, wherein the assignment and the distribution takeplace mapped symbol by mapped symbol or wherein the mapped symbols areassigned before the first and second components of the mapped symbolsare distributed.
 4. The transmitter in accordance with claim 1, in whichthe first and second components are assigned to the interleaving unit,so that each favourable possibility of distributing the first and secondcomponent of a mapped symbol, where the first and second components ofthe mapped symbols are distributed to different interleaving unitsoccurs and do not end up in the same interleaving unit, occurs, for thecodeword, with the quantity being the same for all favourablepossibilities or deviating by a maximum of 50% related to an averagequantity.
 5. The transmitter in accordance with claim 1, wherein thecomponent interleaver is configured for performing an assignment asfollows: assign the first components of a codeword contiguously amongthe interleaving units; and assign the second components of a codewordwith a cyclic repetition of every M*(M−1) mapped symbols to thedifferent interleaving units, wherein M is the number of interleavingunits for a codeword.
 6. The transmitter in accordance with claim 5,wherein the second components are paired and the pairs of the secondcomponents are assigned to the interleaving units with a cyclicrepetition of every (M−1) mapped symbol.
 7. The transmitter inaccordance with claim 1, in which the component interleaver isconfigured for assigning the first and second components in accordancewith an interleaver rule based on: determining the interleaver unit forthe first component of a symbol j as j mod M; and determining theinterleaver unit for the second component of a symbol j as (floor (j/M)mod M−1)+1+j) mod M, wherein mod is the modulo operation, where j is anumber of a mapped symbol in a codeword, M is the number of interleavingunits, and floor is a function rounding down to the nearest integer. 8.The transmitter in accordance with claim 1, in which the componentinterleaver is configured to interleave the I component of symbol j tothe cell with index (j mod M) N+floor (j/M), where N=FEC block length/M,and to interleave the Q component of symbol j to the cell with index((floor (j/M) mod(M−1)+1+j) mod M)*N+floor (j/M), wherein mod is themodulo operation, where j is a number of a mapped symbol in a codeword,M is the number of interleaving units, and floor is the functionrounding down to the nearest integer.
 9. The transmitter in accordancewith claim 1, in which the mapper is configured for generating rotatedmapped symbols in accordance with a rotated constellation mapping rule.10. A receiver for receiving information, comprising: a receiver inputstage for providing a codeword comprising a sequence of interleavingunits, the codeword comprising interleaved mapped symbols, each mappedsymbol comprising a first component and a second component, wherein oneof the first and second components is an in-phase component and theother of the first and second components is a quadrature component,wherein the interleaved mapped symbols are interleaved such that allfirst components and all second components of a codeword have beeninterleaved in accordance with an interleaving rule so that the firstcomponent and the second component belonging to the same mapped symbolare never assigned to one and the same interleaving unit, but areassigned to different interleaving units; a component de-interleaver forstoring the codeword and for de-interleaving in accordance with theinterleaver rule to acquire de-interleaved mapped symbols, each mappedsymbol comprising the first component and a second component belongingto the first component; and a decoder for decoding the de-interleavedmapped symbols to acquire a decoded information unit represented by themapped symbols.
 11. The receiver in accordance with claim 10, in whichthe component de-interleaver is configured to use the de-interleavingrule, so that a mapped symbol is never constructed from two componentsof the same interleaving unit, wherein there exist at least threeinterleaving units
 12. The receiver in accordance with claim 10, inwhich the interleaving rule is so that each favourable possibility,where the first and second components of the mapped symbols aredistributed to different interleaving units and do not end up in thesame interleaving unit, occurs, for a codeword, one or more times, andin which the component de-interleaver is configured to de-interleave inaccordance with the interleaver rule.
 13. The receiver in accordancewith claim 10, in which the interleaving rule is so that all mappedsymbols in a codeword are assigned to all different favourablepossibilities, where the first and second components of the mappedsymbols are in different interleaving units occurs and are not in thesame interleaving unit, for distributing the first and second componentsof the mapped symbols with a predetermined number of occurrences in apseudo-random or deterministic manner and the first and secondcomponents are distributed in accordance with the assignment, whereinthe assignment and the distribution take place mapped symbol by mappedsymbol or wherein the mapped symbols are assigned before the first andsecond components of the mapped symbols are distributed, and in whichthe component de-interleaver is configured to de-interleave inaccordance with the interleaver rule.
 14. The receiver in accordancewith claim 10, in which the component de-interleaver is configured tode-interleave based on the following de-interleaver rule: de-interleavethe I component of received interleaved mapped symbol n to the mappedsymbol with index floor (n/N)+(n mod N)*M, where N=block length/M;de-interleave the Q component of received interleaved mapped symbol n tothe mapped symbol with index (floor (n/N)+M−1−(n mod N) mod(M−1)) modM+(n mod N)*M; where the IU k, with k from 0 to M−1, is composed of thereceived interleaved mapped symbols with indices N*k+0 to N*k+(N−1); andoutput the de-interleaved mapped symbols in the order of their index,wherein mod is the modulo operation, where n is an index of a cell, andM is the number of interleaving units.
 15. A method of transmittinginformation, comprising: generating a plurality of mapped symbols, eachmapped symbol comprising a first component and a second component, oneof the first and second components being an in-phase component and theother of the first and second components being a quadrature componentfrom a codeword; and generating a plurality of interleaving units to betransmitted in a time sequence, the plurality of interleaving unitscomprising at least three different interleaving units, wherein aninterleaving unit comprises a plurality of pairs of first and secondcomponents, wherein the generating a plurality of interleaving unitscomponent interleaver assigns all first components and all secondcomponents of a codeword to the plurality of interleaving units inaccordance with an interleaving rule, so that a I component of a mappedsymbol and the Q component of the same mapped symbol are never assignedto one and the same interleaving unit, but to two different interleavingunits.
 16. A method of receiving information, comprising: providing acodeword comprising a sequence of interleaving units, the codewordcomprising interleaved mapped symbols, each mapped symbol comprising afirst component and a second component, wherein one of the first andsecond components is an in-phase component and the other of the firstand second components is a quadrature component, wherein the interleavedmapped symbols are interleaved such that all first components and allsecond components of a codeword have been interleaved in accordance withan interleaving rule so that the first component and the secondcomponent belonging to the same mapped symbol are never assigned to oneand the same interleaving unit, but are assigned to differentinterleaving units; storing the codeword and de-interleaving inaccordance with the interleaver rule to acquire de-interleaved mappedsymbols, each mapped symbol comprising the first component and a secondcomponent belonging to the first component; and decoding thede-interleaved mapped symbols to acquire a decoded information unitrepresented by the mapped symbols.
 17. A computer program comprising aprogram code for performing, when running on a computer, a method inaccordance with claim
 15. 18. A computer program comprising a programcode for performing, when running on a computer, a method in accordancewith claim 16.